Green manure
The term "green manure" refers to a crop that is grown in order to be incorporated into the soil. These often, but not always, double as cover crops -- crops which are grown as a living mulch. Advantages of green manure * Increase soil biomass * Scavenge nitrogen from decomposing crops, preventing microorganisms from eating it all * Legumes fix nitrogen, further increasing soil nitrogen content * Many also function as cover crops, suppressing weeds and preventing rain-induced leaching and soil erosion from fallow land * Roots will improve soil tilth * Deep-rooted plants draw up nutrients from subsoil * Flowering plants feed and attract bees, which then pollinate nearby crops * May provide forage for livestock Disadvantages of green manure * It forces an area to be unproductive for a period of time (growth of manure + fallow period after turning-in). However, many farming methods require a fallow period. * Lost opportunity to grow carbon crops. * Some crops can exert allelopathic effects for several weeks after they are dug into the soil, necessitating a delay before new crops are planted. Choice of green manure crop * Is the green manure crop related to the crop that will follow it? ** Avoid planting a green manure crop that is closely related to the crop that will follow. * How quickly will the next crop need the nitrogen produced by the green manure crop? ** Try to choose a crop whose speed of nitrogen release matches the needs of the succeeding crop. ** Generally, legumes and mustard release nitrogen quickly after death, whereas grasses release it more slowly * Some crops are allelopathic once dug into the soil, i.e. they will prevent germination of other seeds for several weeks. * How much time do you have before the next crop must be sown? ** No more than 1 season: choose a quick-maturing crop. *** For summer: mustard, phacelia, clover, vetch, fenugreek, yellow trefoil, buckwheat *** For winter: rye, vetch, ryegrass, red clover, sweet clover ** A year or more: alfalfa, sainfoin, red clover, sweet clover, chicory, cocksfoot * What season are you sowing? ** If the crop is being sown late in autumn, rye is a good choice. ** The soil will probably be too cold for nitrogen fixation to occur, so legumes are not a good choice for a quick cold-weather crop as they grow slowly during winter, and their symbiotic nitrogen-fixing bacteria are inactive in cold temperatures. * Should you use a mixture? ** A mixture of a legume and a grass is often advocated, as the legume will fix nitrogen while the grass holds the nitrogen and improves soil structure * What other functions are most important? ** Weed suppression, prevention of leaching and erosion: look at cover crops ** Nitrogen fixation: look at legumes ** Nitrogen retention: look at non-legumes, especially grasses ** Improve the soil tilth: look at grasses and deep-rooted crops. Practical You do not need to wait until the bed is cleared. Instead you can undersow the crop while the previous crop is still standing. Consider mowing once. Advantages: * Controls weeds which may be competing with the crop * Promotes exuberant leafy growth * Delays seed formation, and therefore woodiness The cuttings can be left where they lie (the nitrogen they release may temporarily suppress nitrogen fixation), composted, or used to make silage. It is important to try and grow the crop to flower before digging it in -- for legumes this ensures the maximum amount of nitrogen is fixed (nitrogen starts to be taken out of the root nodules again as the plants form seed). However, don't let it grow beyond the flowering stage into the woody stage -- then it will contain too much carbon and will steal nitrogen from the soil as it rots. If it has reached this stage, it is better to put it onto the compost pile. All green manure must be turned at least 2-3 weeks before planting anything else in the bed. Some green manures are allelopathic after death, meaning that you must wait at least 6 weeks before introducing another crop. Alternatives and variations Jeavons recommends growing the compost crops but not digging them in -- compost them instead once they have reached the woody stage. spring.early: good time to dig in green manure green manure; biomass waste; resource biomass; digger; nitrogen-fixer resource References Category:Product Category:Green manure